A variety of accurate and reliable assays for measuring minute quantities of analyte dissolved in a solution (e.g., hormones in biological fluids) have been produced and described in the literature. Such assays have commonly required, for their proper performance, a rather high degree of technical and mechanical skill in the measurement of small amounts of reagents, in following detailed procedures, and in using sophisticated analytical equipment. There exists a need for a method of qualitatively and desirably at least semiquantitatively detecting, in the field (that is, outside the laboratory environment) the presence or absence of minute quantities of materials on a rapid basis by persons who often may not be technically skilled. For example, tests for various drug levels in human biological fluids such as urine and blood serum desirably should be available to and capable of use by law enforcement personnel or by paramedics or other emergency medical personnel, inasmuch as it is often of great diagnostic benefit to quickly determine the presence or absence of particular drugs in the blood stream. A ready and effective assay is needed for determining whether certain harmful substances are present in food, such as penicillin in milk, marine toxins in seafood, etc. Needed also are effective field tests for determining whether pollutants exceed particular concentrations (e.g., salts of mercury in lake water).
The present invention provides apparatuses and methods which are unique in that they can in large measure be readily and easily used or performed in the field by minimally trained personnel.